This disclosure generally relates to towed streamers for use in acquiring seismic data, and more specifically, to solid streamers and methods of manufacturing same.
Seismic exploration involves surveying subterranean geological formations for hydrocarbon deposits. A seismic survey typically involves deploying seismic source(s) and seismic sensors at predetermined locations. The sources generate seismic waves, which propagate into the geological formations creating pressure changes and vibrations along their way. Changes in elastic properties of the geological formation scatter the seismic waves, changing their direction of propagation and other properties. Part of the energy emitted by the sources reaches the seismic sensors. Some seismic sensors are sensitive to pressure changes (hydrophones), others to particle motion (e.g., geophones), and industrial surveys may deploy only one type of sensors or both. In response to the detected seismic events, the sensors generate electrical signals to produce seismic data. Analysis of the seismic data can then indicate the presence or absence of probable locations of hydrocarbon deposits.
Some surveys are known as “marine” surveys because they are conducted in marine environments. However, “marine” surveys may be conducted not only in saltwater environments, but also in fresh and brackish waters. In one type of marine survey, called a “towed-array” survey, an array of seismic sensor-containing streamers and sources is towed behind a survey vessel.
Streamers are long cables that house various sensor networks and other devices useful in the acquisition of seismic data. Streamers may be manufactured as liquid-filled streamers or solid streamers. Prior art solid streamer cables are often constructed with a central core with transmission and power bundles that are continuous through the streamer section (a segmented portion of a streamer cable). The transmission and power bundles are typically connected to electronics modules between the streamer sections through end connectors. Also within a streamer section, there is a need to connect distributed sensors and (if present) sensor electronics by wires to transmit power and data to the electronics modules.
In solid streamer cables, it is often a challenge to have wires run external to the stress member armoring because the bending forces experienced by the streamer cable impart local deformations that may introduce tensile or compressional stress in the wires. These stresses may eventually lead to deformations and/or breaks of the wires. The common way in the prior art to remove or reduce this effect is to twist the wires with a certain lay length around the stress member, which thus cancels the compressional and tensional forces experienced by the wires. However, the manufacturing and repair processes associated with utilizing twisted sensor wires and/or local electronics network wires are complicated.
FIG. 1 illustrates a prior art arrangement in which a solid streamer cable 10 includes a central core 12 having a transmission bundle 14 surrounded by a strength member 16. The central core 12 is typically pre-fabricated before adding sensors and/or sensor electronics. Local wiring 18, which is used to connect the sensor and sensor electronics, is also disposed in the streamer cable 10 inside of a polymer body 20 and a skin 22. The typical way to dispose the wiring 18 within the streamer cable 10 is to twist the wiring onto the central core 12 with a certain lay-length (or pitch) to allow for tensile cycling and bending of the streamer cable 10 without generating high stresses in the wires. Wiring layers in prior art solid cables are often pre-made with the central core 12.
One of the drawbacks associated with the prior art solid cable 10 of FIG. 1 is that it complicates the manufacturing process by making it difficult to access and thereby connect the local wiring 18 to the sensors and/or sensor electronics. More particularly, it is difficult to open the local wiring 18 and cut the correct wires at the desired inline and rotational location. It is also challenging to obtain the desired slack in the wiring 18 to robustly establish connection between the wiring and the sensors and/or sensor electronics. In addition, connection of the wiring 18 to the sensors and/or sensor electronics has to be done late in the assembly process of the cable 10. This makes the manufacturing process complex as many units have to come together at the same production step.